1. Field of the Invention
The present invention relates to improvements in an extraction/insertion type soot blowing apparatus.
2. Description of the Prior Art
An extraction/insertion type soot blowing apparatus is an apparatus which is inserted into a combustion chamber of a heat-exchanger or the like to blow air or steam at a high pressure against a deposit (23) adhering to a heat-absorbing portion (24) (water-wall tubes or the like) contiguous to wall surface (22) to remove the deposit, as shown in FIG. 6. This promotes heat absorption by the heat-absorbing portion (24) and improves efficiency of heat recovery.
One example of an extraction/insertion type soot blowing apparatus in the prior art is shown in FIG. 6. Reference numeral (013) designates a head valve, and feed and interruption of injection medium (air, steam, or the like) is carried out by this head valve (013). An injection (or discharge) medium is discharged from a nozzle provided at a tip end of a lance tube (015) through a feed pipe (014). The lance tube (015) simultaneously rotates and moves in the axial direction, while discharging medium against a deposit (23), in order to remove the deposit (23) adhering to the surface of the heat-absorbing portion (24).
Driving of the above-described lance tube (015) is effected in the following manner. That is, rotation of a power source (01) is reduced in speed by a gear box (02), and a lead screw (06) is rotated via gears (03), (04) and (05). The lead screw (06) moves a gear box (08) in its axial direction. Within the same gear box (08), the lance tube (015) and a gear (012) are directly connected with each other, and the lance tube (015) moves in the axial direction as interlocked with the gear box (08). On the other hand, rotation of the lance tube (015) is effected by rotating the gear (012) via a long key slot provided along the entire length of the lead screw (06), a key (not shown) and a gear (011).
In addition, starting and stopping of the flow of the injection medium is carried out by the head valve (013) as described above, and opening and closing of the same valve (013) is effected by actuating a valve opening/closing cam (017) by means of a dog (016) provided on the gear box (08) when the gear box (08) moves in the axial direction, and valve moving levers (019) and (020) via a connecting rod (018). More particularly, provision is made such that when the dog (016) on the gear box (08) has reached a point P, discharge is commenced, and when it continues to move further (advance) in the axial direction and has reached a point Q, the power source (01) reverses and the gear box (08) moves in the direction of retreat. When the gear box (08) has reached the point P again, the discharge terminates. Thus, discharge of the medium occurs over the range from a point R to a point S, as depicted in FIG. 6.
The above-described prior art extraction/insertion type soot blowing apparatus has the following shortcomings:
1) Since the lance tube (015) advances and retreats in the axial direction by rotating and while discharging the discharge medium, the soot removing power (momentum) is not stable over the range of from the point R to the point S. More particularly, as the discharge nozzle of the lance tube (015) moves between the point R and the point S, the distance between the nozzle and the heat-absorbing surface to be cleaned varies, and further a circumferential velocity of the discharge medium at the surface to be cleaned also varies. Consequently, the soot removing effects are non-uniform.
2) The lance tube (015) rotates several revolutions while moving over the range from the point R to the point S. Therefore, a discharge angle cannot be limited, and hence, even if it should become necessary to avoid injection at a corner portion of a combustion chamber or the like, it cannot be done.
3) The time it takes for the lance tube (015) to move from the point T to the point R is long, and so, the tip end portion of the lance tube (015) becomes overheated when exposed to a high-temperature gas before it reaches the point R. Also, since the discharge medium flows into the tip end portion when it has reached the point R, the tip end portion of the lance tube (015) is quickly cooled and thus is subjected to a thermal shock, so as to sometimes cause damage to the nozzle.
4) Due to the fact that the moving range (from the point T up to the point S) of the lance tube (015) is long, the entire apparatus is long and requires a large installation space.
5) In addition to the poor soot removing performance as described in paragraph 1) above, the discharge time is long and a large amount of the discharge medium is consumed.
6) In relation to the disadvantage described in paragraph 2) above, since the discharge medium is discharged at a high temperature toward the heat-absorbing portion (the water-wall tubes) at a predetermined angle, sometimes even after removal of the soot, the heat-absorbing portion (the water-wall tubes) are liable to be thermally damaged.